DE4137864C2 - Process for the catalytic oxidation treatment of waste water - Google Patents

Description

The invention relates to the catalytic oxidation of Ab water pollutants with the addition of hydrogen peroxide.

A number of wastewater treatment processes are known from the prior art, with the tendency towards catalytic oxidation having increased due to the at least partially successful degradation of poorly degradable organic pollutants. These partly toxic or ecotoxic compounds, among which there are numerous household chemicals, represent an almost insoluble problem, especially for municipal wastewater treatment plants with mainly mechanical-biological cleaning stages. Oxidation using hydrogen peroxide and UV radiation significantly reduces the Toxicity, increased biodegradability and easier separation of the ingredients achieved. A disadvantage of this process is the still very significant addition of H ₂ O ₂ and the measurement and control problems that arise as a result, as well as the poor utilization of UV radiation in the cloudy or strongly colored wastewater, which is therefore hardly deeper than in the immediate surface layer can penetrate, and the therefore disproportionately high energy expenditure required.

For working with H ₂ O ₂ and UV, DE 40 06 234-A1 should be used as an example, in which it is proposed to reduce the excess of hydrogen peroxide by removing a partial stream and a further partial stream, and thereby the turnover potential of a reagent solution in a partial stream to measure and thus control the H ₂ O ₂ addition.

Oxidation processes are also known, in which a Mixture of hydrogen peroxide and Fe-II salts, which as Fentons reagent is known, is used (Environment, 1981, Pp. 482-487).  

DE 29 27 911-A1 describes a wastewater treatment process known in the presence of catalytic transition metal compounds implemented the waste water pollutants with H₂O₂ become, d. H. the COD content is controlled solely by the amount of H₂O₂ supplied.

In J. Am. Chem. Soc. 104 (1982), pp. 6450-52 are tri-iron complexes for the catalytic epoxidation of olefins. There is no evidence of wastewater treatment processes.

JP 2-144 194-A (Abstract in Patents Abstracts of Japan C-750, Vol. 14 / No. 386, Sekt. C) discloses the addition of proteins such as α-amylase in the presence of H₂O₂ to increase the removal rate of phenols and aromatic amines.

DE 38 35 938-A1 relates to a tubular reactor as a separate one Defined system with reaction-dependent training of Pipe section, depending on reaction times and quantities.

From Chem. Abstracts, vol. 107, 1987, p. 418, 107: 140 779p is the use of oxidation catalysts (including Fe ³⁺ and Mn ²⁺ ) to improve the effect of H₂O₂ or O₃ in the removal of humic substances Known water.

In CH 599 059-A5 there is a system for wastewater treatment made of water-insoluble catalysts and ozone / air.  

DE 39 32 174-A1 states with reference to research results that the AOX content cannot be reduced below 1 mg / l by the known oxidation with hydrogen peroxide and the catalytic addition of Fe ²⁺ . It is proposed to use an oxidizing agent (H ₂ O ₂ ) for the oxidation of Fe ²⁺ to Fe ²⁺ as well as precipitated pyrogenic silica in addition to Fe ²⁺ . Such methods show good results, especially in the case of waste water with organic halogen-containing compounds, but have the same disadvantages as all processes which only use hydrogen peroxide as the oxidant. In addition, the anion of the iron (II) salt increases the salt load of the waste water undesirably increased.

As already mentioned, wastewater treatment processes using catalysts are also known. For example, DE 39 38 835-A1 discloses an oxidation process of biodegradable, toxic, organic impurities using atmospheric oxygen, which uses a CuO / ZnO / CrO ₂ / Al ₂ O ₂ catalyst as a catalyst. However, this requires a considerable additional outlay on equipment and, in addition, the addition of the catalyst occurs as an additional problem due to the considerable amount of suspended matter.

DE 33 16 265-A1 describes an oxygen treatment process described at elevated temperature and pressure, for which the wastewater co-catalysts such as benzo and naphthoquinones be used.

The invention has for its object to achieve a sufficient catalytic oxidation of poorly degradable pollutants in the wastewater with only small additions of H ₂ O ₂ .

According to the invention, the process for the catalytic oxidation treatment of waste water is characterized in that both the oxidation potential of further oxidizing agents, especially atmospheric oxygen, are used, and the generation of the oxidatively particularly effective radicals, in particular the hydroxyl radical HO ^· , is made more effective. According to the invention, a wastewater contaminated with organic oxidizable compounds, in particular amines and / or (poly) phenols-containing wastewater is treated simultaneously with hydrogen peroxide and gaseous oxygen or ozone in the presence of a soluble catalyst which prevents the formation of oxygen-containing radicals of high redox potential and high reactivity catalyzed, selected from the group of manganese or iron complexes of the type

[O (Fe ^III ) ₂M ^II (acetate) ₆ (H₂O) ₃] (M: Fe ²⁺ , Mn ²⁺ )

and

[O (Fe ^III ) ₃ (acetate) ₆ (H₂O) ₃] X (X = monovalent anion).

X is preferably not the salt load of the waste water or low-stress anion, especially acetate.

In this process, hydrogen peroxide solution is used depending on determined chemical oxygen demand (COD or COD), in an amount of 0.2 to 0.95 vol .-% of the waste water added.

Oxygen becomes up to a volumetric gas content (Volume fraction of the gas in the volume flow; see Mayinger, F. "Flow and heat transfer in gas-liquid mixtures", Springer Verlag Vienna, New York 1982, p. 32) by 0.05 to 0.2 of the waste water, preferably 0.08 to 0.12 of the Discharged sewage. It is advantageous that the oxygen is supplied in the form of air, because in this way a very cheap oxygen supply becomes possible. The ent in the air nitrogen as an inert gas has no influence on the Method. The air additive is the oxygen content of the air and the desired amount of oxygen to be added sen.

The catalyst is used in an amount of 0.05 to 3 mol%, preferably 0.1 to 1.5 mol%, based on hydrogen per oxide, added.

The released from the above catalysts Iron (III) or manganese (III) ions are already in the required phosphate precipitation as iron (II) - or Manganese (III) phosphates entrained, and that from the ligand Acetate derived from the biological bacteria Cleaning level to be consumed. Hence the use of this Catalysts are particularly cheap. Preferred catalysts are of the type

[O (Fe ^III ) ₂Fe (acetate) ₆ (H₂O) ₃]

which can also be called iron (II / III) acetate.

To the required mixing of oxygen or air To obtain in the wastewater is the use of, for example Bubble column reactors useful. According to the invention particularly However, it is advantageous to add oxygen or air drove into the sewage system before the waste water entered to make a treatment plant, the air being sour fabric carrier with an empty tube flow rate of about 1 m / s to about 10 m / s, preferably 3 to 8 m / s, ins special 4 to 7 m / s in the sewage supply channels or -pipes is introduced so that there is a waste water- Mixture flow rate in the range of about 0.5 to 5 m / s, preferably from 1 to 3.5 m / s. Under "empty pipe speed" is the speed understood that would assume in gas if it was alone and evenly distributed in the pipe over the entire pipe cross-section flows (see also Mayinger, F. "Flow and heat transfer in gas Liquid Mixtures ", Springer Verlag Vienna, New York, 1982, P. 32). The initiation of oxygen or air is a special feature of the Invention at some distance from the sewage to carry out a system of action that is sufficient according to the selected flow velocities and the carried oxygen volume the formation of insoluble Sludges from the pollutants or their conversion into to ensure micro-biodegradable products so that they separated when entering the plant or accordingly can be treated further.

An oxidation of organic toxic and / or poorly degradable substances can only be achieved if the activation energies required for this are sufficiently reduced by suitable reaction conditions and if oxidative species with a high redox potential and high reactivity are generated in sufficient concentrations by a suitable reaction procedure. In the process according to the invention, this takes place in that, on the one hand, catalytic cleavage of the hydrogen peroxide, inter alia, to give hydroxyl radicals, and, on the other hand, oxygen, which is normally not very reactive as a diradical, under the action of the catalysts according to the invention in the form of HO₂ ^- and O₂ · ^- for reaction brought. This keeps a radical chain mechanism going since oxygen is present in the wastewater in sufficient quantities due to the air supply.

According to the invention, the oxidative potential can be increased again by supplying ozone. In any case, there is a sufficient amount of OH radicals (with the particularly high redox potential of 2.80 V), HO ₂ - from oxygen (redox potential 0.87 V) and possibly ozone (redox potential 2.08 V) to convert the oxidizable pollutants into microbially degradable and / or less toxic products. It is primarily the task of oxygen to further oxidize the pollutants oxidized by the OH radical or ozone to the desired insoluble or microbially degradable end products.

Under these conditions, the sewage treatment plants become strong annoying, toxic for bacteria and hardly affected by them buildable amines and poly (phenols) especially to semiquinones oxidized, which immediately condensation reactions with yet unchanged phenols or amines enter with formation inophenin-like, high-molecular, insoluble condensate tion products that can be easily separated as sludge. The method according to the invention is therefore particularly useful Presence of the amines and phenols mentioned, where primarily conversion reactions are expected, but less so Molecular breakdowns, such as in treatment organic halogen compounds according to DE 39 32 174-A1 and EP 4 19 842-A1 are to be expected.

In order to carry out the oxidation process of the invention, intensive mixing of waste water and oxygen, preferably air, is required, as is expressed by the speeds given. This can be achieved particularly advantageously if the oxygen in the form of air is introduced into the wastewater a certain distance before entering the wastewater treatment plant. This is done simultaneously with the addition of hydrogen peroxide and the catalyst. A change in the water speed also results in a corresponding change in the air speed in order to achieve the desired turbulent mixing of the two phases. The oxidation reactions already taking place in the waste water supply lines in this way lead to microbially degradable and insoluble substances. As already stated, the oxidation reactions taking place in the pipe when using iron and manganese catalysts lead to substances that are precipitated in the wastewater treatment plant as Fe ³⁺ or Mn ³⁺ phosphates during phosphate precipitation (the stability constants of the complexes allow this), and the acetate ligands can be processed by the bacteria of the biological purification stage.

In addition to the advantages mentioned, the catalysts used according to the invention have the advantage that they, as a soluble molecularly disperse catalyst, cannot be deactivated by any suspended matter. The catalysts can be produced by known processes, such as those described in e.g. B. by Blake et al. in J. Chem. Soc. Chem. Commun., 1982, pp. 1247-1249. Essentially the Fe ³⁺ from salts is converted into Fe (OH) ₃ and the hydroxide is again dissolved in concentrated acetic acid. From the cost side, these catalysts are therefore also very cheap.

The invention provides a simple to use apparatus for the oxidation process, which offers particular advantages because of the use of cheap and always available atmospheric oxygen, low levels of H ₂ O ₂ and catalyst and low energy requirements. The oxidation of waste water pollutants started with the method according to the invention as a radical chain mechanism enables effective through oxidation of the pollutants with atmospheric oxygen and leads to improved waste water treatment.

The invention is illustrated by examples. The accompanying drawing shows in

Fig. 1 flow diagram of the method according to the invention.

The inflow of waste water via line 1 goes into metering station 2 , to which hydrogen peroxide, air and catalyst are fed via line 3 . At the station 4 there is a sludge separation, and the transport pipe 5 also represents the actual reaction space for the mixture of waste water, air, catalyst and H₂O₂. Ozone generator 6 , optionally arranged on this reaction space, can be used to supply ozone. Line 7 is the discharge line to the sewage treatment plant.

example 1

10 cm ^{3 of} a phenolic wastewater from azo dye production, containing inter alia H acid, picraminic acid, p-nitraniline, non-coupled intermediate stages and finished dye, were mixed with 1% by volume of one percent hydrogen peroxide and with 10 mg of catalyst [O (Fe ^III ) ₃ (acetate) ₆ (H ₂ O) ₃ ] acetate. This mixture was treated in a reactor with a height of 250 mm and a diameter of 25 mm with bottom frit while passing compressed air (2 l / h). The decrease in the concentration of phenolic components was detected colorimetrically at a wavelength of 340 nm. The extinction rapidly decreased from E = 3.036 to E = 2.925 within 30 min and remained constant after 30 minutes.

Example 2

10 cm ^{3 of} a waste water from insecticide production, containing, inter alia, chlorobenzene, dimethyl-thiophosphoric acid chloride and p-nitrophenol sodium salt, was mixed with 1.7 cm ^{3 of} 30% hydrogen peroxide and 10 mg of Fe (III) acetate complex and under for 2 hours Passage of compressed air (2 l / h) treated, the color of the solution initially changing from yellow to brown and then gradually lightening again with the formation of precipitation and cloudiness. The degradation of phenolic compounds was demonstrated by HPLC.

Claims (12)

1. A process for the catalytic oxidation treatment of waste water, in particular waste water containing amines and / or (poly) phenols, in the presence of transition metal compounds, characterized in that waste water contaminated with organic compounds is treated simultaneously with hydrogen peroxide and gaseous oxygen or ozone in the presence a soluble catalyst selected from the group of the iron or manganese salts of the type [O (Fe ^III ) ₂M ^II (acetate) ₆ (H₂O) ₃] (M: Fe ²⁺ , Mn ²⁺ ) and [O (Fe ^III ) ₃ (acetate) ₆ (H₂O) ₃] X (X = monovalent anion). 2. The method according to claim 1, characterized in that Hydrogen peroxide solution in an amount of 0.2 to 0.95 vol .-% of the waste water is added. 3. The method according to claim 2, characterized in that Hydrogen peroxide solution in an amount of 0.5 to 0.95 vol .-% of the waste water is added. 4. The method according to claim 1, characterized in that the Oxygen is supplied in the form of air. 5. The method according to claim 4, characterized in that air is supplied in an amount of 0.05 to 0.5 m ³ per m ^{3 of} waste water. 6. The method according to claim 4, characterized in that the Air supply with an empty pipe speed of 1 m / s to 10 m / s at a waste water flow rate of 0.5 up to 5 m / s.   7. The method according to claim 6, characterized in that the Empty pipe speed is 3 m / s to 8 m / s. 8. The method according to claim 6 or 7, characterized in that the flow rate of the waste water is 1 m / s to 3 m / s is. 9. The method according to any one of claims 1 to 8, characterized in that the catalyst is [O (Fe ^III ) ₂ Fe (acetate) ₆ (H ₂ O) ₃ ]. 10. The method according to any one of claims 1 to 8, characterized in that the catalyst is [O (Fe ^III ) ₃ (acetate) ₆ (H ₂ O) ₃ ] (acetate). 11. The method according to any one of claims 1 to 10, characterized in that the addition of H ₂ O ₂ , catalyst and oxygen or ozone at one of the wastewater treatment system is carried out before the metering point. 12. The method according to claim 11, characterized in that the addition as far as before the wastewater treatment plant, that the sewage pipes are used as an oxidation reactor and the resulting oxidation products as sludge or microbiologically degradable products in the system can kick or the sludge if necessary abge beforehand can be separated.